Many existing antennas include resonator elements. The resonator elements are often tuned by introducing phase delay elements that have high cost or, more recently, by tuning anisotropic liquid crystals (LCs). For example, LCs have been used as the tuning element in metamaterial holographic antennas.
The use of LCs adds complexity to their implementations in various designs. For example, LCs may be limited in the speed at which they can be switched, operational temperature ranges, and long term environmental reliability. More specifically, because of the added complexity in using an LC as a tuning medium for antennas means that system designers have to deal with issues regarding: temperature dependence, RF losses, switching speed, reliability, and capacitive tuning. With respect to temperature dependence, the LC must be warmed to meet tracking rates for cold operation, while its warm operation is limited by the LC clearing point. With respect to switching speed, the LC is a long-chain hydrocarbon molecule that is being physically rotated in a viscous medium, and as a result, the switching speeds with LC are limited to the 1-10 msec range. With respect to reliability, some types of LCs are very sensitive to ultraviolet (UV) light, water, and heat. Also, the voltage holding ratio is shown to degrade significantly with accelerated aging, which adds complexity into the design to ensure reliable performance and operation in the field. In view of these issues, it may be desirable to seek alternatives to LCs for use in antennas.